Minimal libc

The most basic C library, named “minimal libc”, is part of the Zephyr codebase and provides the minimal subset of the standard C library required to meet the needs of Zephyr and its subsystems, primarily in the areas of string manipulation and display.

It is very low footprint and is suitable for projects that do not rely on less frequently used portions of the ISO C standard library. It can also be used with a number of different toolchains.

The minimal libc implementation can be found in lib/libc/minimal in the main Zephyr tree.

Functions

The minimal libc implements the minimal subset of the ISO/IEC 9899:2011 standard C library functions required to meet the needs of the Zephyr kernel, as defined by the Coding Guidelines Rule A.4.

Formatted Output

The minimal libc does not implement its own formatted output processor; instead, it maps the C standard formatted output functions such as printf and sprintf to the cbprintf() function, which is Zephyr’s own C99-compatible formatted output implementation.

For more details, refer to the Formatted Output OS service documentation.

Dynamic Memory Management

The minimal libc uses the malloc api family implementation provided by the common C library, which itself is built upon the kernel memory heap API.

Error numbers

Error numbers are used throughout Zephyr APIs to signal error conditions as return values from functions. They are typically returned as the negative value of the integer literals defined in this section, and are defined in the errno.h header file.

A subset of the error numbers defined in the POSIX errno.h specification and other de-facto standard sources have been added to the minimal libc.

A conscious effort is made in Zephyr to keep the values of the minimal libc error numbers consistent with the different implementations of the C standard libraries supported by Zephyr. The minimal libc errno.h is checked against that of the Newlib to ensure that the error numbers are kept aligned.

Below is a list of the error number definitions. For the actual numeric values please refer to errno.h.

group system_errno

System error numbers Error codes returned by functions.

Includes a list of those defined by IEEE Std 1003.1-2017.

Defines

errno

EPERM: Not owner.

ENOENT: No such file or directory.

ESRCH: No such context.

EINTR: Interrupted system call.

EIO: I/O error.

ENXIO: No such device or address.

E2BIG: Arg list too long.

ENOEXEC: Exec format error.

EBADF: Bad file number.

ECHILD: No children.

EAGAIN: No more contexts.

ENOMEM: Not enough core.

EACCES: Permission denied.

EFAULT: Bad address.

ENOTBLK: Block device required.

EBUSY: Mount device busy.

EEXIST: File exists.

EXDEV: Cross-device link.

ENODEV: No such device.

ENOTDIR: Not a directory.

EISDIR: Is a directory.

EINVAL: Invalid argument.

ENFILE: File table overflow.

EMFILE: Too many open files.

ENOTTY: Not a typewriter.

ETXTBSY: Text file busy.

EFBIG: File too large.

ENOSPC: No space left on device.

ESPIPE: Illegal seek.

EROFS: Read-only file system.

EMLINK: Too many links.

EPIPE: Broken pipe.

EDOM: Argument too large.

ERANGE: Result too large.

ENOMSG: Unexpected message type.

EDEADLK: Resource deadlock avoided.

ENOLCK: No locks available.

ENOSTR: STREAMS device required.

ENODATA: Missing expected message data.

ETIME: STREAMS timeout occurred.

ENOSR: Insufficient memory.

EPROTO: Generic STREAMS error.

EBADMSG: Invalid STREAMS message.

ENOSYS: Function not implemented.

ENOTEMPTY: Directory not empty.

ENAMETOOLONG: File name too long.

ELOOP: Too many levels of symbolic links.

EOPNOTSUPP: Operation not supported on socket.

EPFNOSUPPORT: Protocol family not supported.

ECONNRESET: Connection reset by peer.

ENOBUFS: No buffer space available.

EAFNOSUPPORT: Addr family not supported.

EPROTOTYPE: Protocol wrong type for socket.

ENOTSOCK: Socket operation on non-socket.

ENOPROTOOPT: Protocol not available.

ESHUTDOWN: Can’t send after socket shutdown.

ECONNREFUSED: Connection refused.

EADDRINUSE: Address already in use.

ECONNABORTED: Software caused connection abort.

ENETUNREACH: Network is unreachable.

ENETDOWN: Network is down.

ETIMEDOUT: Connection timed out.

EHOSTDOWN: Host is down.

EHOSTUNREACH: No route to host.

EINPROGRESS: Operation now in progress.

EALREADY: Operation already in progress.

EDESTADDRREQ: Destination address required.

EMSGSIZE: Message size.

EPROTONOSUPPORT: Protocol not supported.

ESOCKTNOSUPPORT: Socket type not supported.

EADDRNOTAVAIL: Can’t assign requested address.

ENETRESET: Network dropped connection on reset.

EISCONN: Socket is already connected.

ENOTCONN: Socket is not connected.

ETOOMANYREFS: Too many references: can’t splice.

ENOTSUP: Unsupported value.

EILSEQ: Illegal byte sequence.

EOVERFLOW: Value overflow.

ECANCELED: Operation canceled.

EWOULDBLOCK: Operation would block.